US6490027B1 - Reduced noise optical system and method for measuring distance - Google Patents

Abstract

A reduced noise optical system is provided for use in measuring distance, range-finding and scanning. The system comprises at least one lens, at least one receiver operably positioned to receive a return beam of light reflected from an object and a limiting aperture operably aligned with the lens to limit the signal, and thus the noise, transmitted in the return beam.

Description

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/145,811, entitled “Improved Optical System for Noise Reduction in Aiming, Range-finding and Scanning Systems,” filed Jul. 27, 1999, the entire disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to optical systems for use in distance measurement or range-finding devices. More particularly, this invention relates to single beam optical systems in range-finding and measurement devices that have improved signal-to-noise ratios.

BACKGROUND OF THE INVENTION

Range-finders are commonly used to determine distances. In current applications of range-finders, the size, weight and cost of the range-finding system may typically be ignored. Conventional range-finding systems are used to determine distances for agriculture, aviation and nautical applications.

Although these systems are adequate for current uses, simultaneous reductions in all four dimensions of size, weight, complexity and cost could enhance distance measuring or range-finding systems for broader or mass market uses. Furthermore, existing dual beam systems also use costly, unwieldy methods for reducing signal-to-noise ratio of the received data signal.

These systems typically employ software applications to overcome signal degradation effects. These software applications require extending the data acquisition interval through signal averaging or other signal conditioning techniques. Such increases in the data acquisition intervals limit the usefulness of such devices.

Optical spatial filtering techniques have previously been used to improve the signal to noise ratio of holographic and microscopic systems (e.g. so-called “confocal” microscopes). However, the application of these techniques to distance measuring or range-finding systems for the purposes of reducing the overall system size, weight, complexity and cost would be desirable.

It would further be desirable to provide a means and method for reducing noise within a range-finding system at a low cost.

It would further be desirable to provide a means and method for reducing noise within a range-finding system that is compatible with optical systems that integrate other optical technologies.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of one embodiment of an optical system of the present invention;

FIG. 2 is a schematic view of a prior art optical system;

FIG. 3 is a schematic view of a second embodiment of an optical system of the present invention as used in a single-beam range-finding or sighting system;

FIG. 4 is a schematic view of a third embodiment of an optical system of the present invention as used in a dual-beam range-finding or sighting system; and

FIG. 5 is a schematic view of another embodiment of an optical system of the present invention as used in a in a scanning system.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

Referring now to FIG. 1, one embodiment of a reduced noiseoptical system100 is shown. Such an optical system may be used for distance measurement or range-finding purposes.Optical system100 comprises atransmit source112 for transmitting an outbound beam oflight114.System100 also includes alens116 through which the beam of light passes.System100 further comprises areceiver122 for receiving a return beam oflight124 from atarget190.System100 also includes alimiting aperture150. Thelimiting aperture150 enables thesystem100 to utilize the focusing properties of thetransmit source112 to greatly increase the signal to noise ratio of the data signal orreturn beam114 eventually received atreceiver122. In one embodiment,receiver122 may be a screen.Receiver122 may be any suitable material for receiving light, such as, for example, semiconductor photo diodes, photo cells, biological optical systems, radio receive systems, photo tubes and microwave receivers.

Insystem100, transmitsource112 may emit a linearly polarizedoutbound beam114 of light. Transmitsource112 may be any source which emits light, such as, for example, a laser diode. It is also typical, though not required, that the emitted polarization type of thelight114 be fixed with respect to time, as is the orientation of the polarization. Alternatively, transmitsource112 may emit non-polarized or non-linearly polarizedlight114, but this will increase loss oflight114,124 from the system.

“Light” may include but is not limited to: non-polarized light; polarized light of elliptical, circular, linear or other orientation; radiation from sources emitting electromagnetic radiation in other than visible portions of the electromagnetic spectrum or any source of electromagnetic radiation that can emit polarized radiation. Polarized light may be defined as light in which the motion of the wave of light is confined to one plane or one direction.

Outbound light beam114 next passes throughlens116 alongoutbound beam path118. Theoutbound beam114 hits a target190 (an object in space such as, for example, a building, a bar code on the building or an identification unit mounted on the building). Theoutbound beam114 is reflected from the target and returns to thesystem100 via thesame beam path118. The transmittedlight114 is now returnbeam124 which returns to thereceiver122.

Return beam124 now passes throughlens116. In alternative embodiments of the invention,return beam124 may pass through a second lens.Return beam124 may also return toreceiver122 along a different beam path.

Return beam includes reflected light fromtarget190. Howeverreturn beam124 also includes light reflected from objects atpositions192 and194.

As seen in FIGS. 1 and 2, onceoutbound light beam114 leaveslens116 on the way to target190,light beam114 may encounter blockages in thebeam path118 such as the blockage shown at192. Additionally,return beam124 may also encounter other objects in thebeam path118 such as the object shown at194. These blockages greatly reduce the ability ofreceiver122 to efficiently collect and control thereturn beam124.

Examples of such blockages could be rain droplets, windows, trees, etc. that are situated between thetransmit source112 and thetarget190. These blockages serve to obscure the target and produce erroneous signals at thereceiver122. Furthermore, since thebeam path118 may pass through or past such obstructions more than once, the effects of these blockages on theoutbound beam114 orreturn beam124 may be doubled. As FIG. 2 shows, an image ofblockage192 may be received byreceiver122 atposition282, thereby blurring the image oftarget190 received by receiver atposition280.

It is also possible that erroneous signals could be produced by structures, vehicles, rain, other weather conditions or other objects existing spatially beyond the target position relative to the transmit system. One such example is shown asobject194 inbeam path118. The proximity of such anobject194 to thebeam path118 may allow theobject194 to be misidentified by thereceiver122 as thetarget190. As withblockage192,object194 may also create scattered light along thebeam path118. This scattered light may raise the noise floor and lower the signal to noise ratio of the received data signal. As FIG. 2 shows, an image ofobject194 may be received byreceiver122 atposition284, thereby blurring the image oftarget190 received by receiver atposition280.

The reflected optical beams from192 and194 at these different positions creates a blur of light at thereceiver122. Thus the image oftarget190 shown in FIG. 2 at280 is blurry.Blur circle280 may be an image oftarget190 as received byreceiver122.Blur circle280 may be assigned a diameter X. The diameter of this blur circle is dependent on the distance of the different obstructions and their receiver-perceived relative intensity.

Referring to FIG. 1,blur circle180 is shown to have a diameter which is less than X.Blur circle180 may be an image oftarget190 as received byreceiver122 in theoptical system100 of the present invention. The diameter of this blur circle is dependent on the distance of the different obstructions and their receiver-perceived relative intensity.

The diameter ofblur circle180 is reduced in size compared to the diameter ofblur circle280 becauseoptical system100 incorporates limitingaperture150. Significant noise power may be encompassed by the blur circle. The frequency mapping of such noise typically indicates that higher frequency components of light are bent at greater angles and are therefore more readily eliminated from the detector's collection by insertion of a limiting aperture.

System100 incorporates spatial filtering of thereturn beam124 to reduce unwanted, spurious noise components from the optical data signal before the signal is converted to an electrical signal byreceiver122.

Limitingaperture150 is any appropriate size forsystem100. In one embodiment, limitingaperture150 comprises an aperture oropening152 within anaperture disk154.Aperture150 withinsystem100 is optically placed so as to reduce the diameter X of the blur circle on while simultaneously limiting the noise spectrum incident onreceiver122. The maximum throughput of the aperture occurs for those rays from objects at a particular distance that come to a focused spot at the aperture. Other rays emanating from other objects, at other distances, will be attenuated (except for those that propagate directly on-axis) by a great extent. For example, in FIG. 1,aperture150 limits the rays emanating fromblockage192 atposition182.Aperture150 also limits the rays emanating fromobject194 atposition184.

In one embodiment, limitingaperture150 is at or near the focal point of thelens116. The position of limitingaperture150 is intended to optimize the ratio between the spot size oftarget190 and the spot size of ablockage192 or anobject194. Such positioning allows for maximum filtering efficiency. For example, iftarget190 is idealized as a dot in space, limitingaperture150 may be positioned so that its focused spot size would be very small atreceiver122. With such positioning, the diameter of theunintended objects192,194 will be larger than that of thetarget190.

The performance increase from use ofaperture150 allows the use of smaller, less expensive, optics as well as reducing the need for error correcting software control algorithms that, in prior art, limit the data acquisition speed of the system.

Light sources typically used in aiming, range-finding and scanning systems display advantageous characteristics that allow for the design of optimized transmission systems. Typically such light sources emit polarized light, of elliptical, circular or linear orientation or a mixture thereof. Furthermore it is typical, though not required, that the emitted polarization type or orientation of the polarization is fixed with respect to time. Such sources may emit un-polarized light. This invention may be embodied in a way so as to reduce any dependence on the polarization of the light sources. Alternatively, it may be advantageous to embody the invention to take advantage of the polarization properties of the transmit sources.

For example, FIG. 3 shows a single-beam embodiment of anoptical system300 in accordance with the present invention.Optical system300 takes advantage of the polarization properties of transmitsource312 to reduce the size of the system. Transmitsource312 emits a linearly polarizedoutbound beam314 of light. Transmitsource312 may be any source which emits light, such as, for example, a laser diode. It is also typical, though not required, that the emitted polarization type of the light314 be fixed with respect to time, as is the orientation of the polarization. Alternatively, transmitsource312 may emit non-polarized or non-linearlypolarized light314, but this will increase loss oflight314,324 from the system.

Outbound light314 then passes throughpolarization selector optic313. This optic313 is constructed and positioned so as to minimize loss and aberration of the transmittedbeam314.Polarization selector optic313 may be any optic that is capable of differentiating between several polarizations of light.Polarization selector optic313 may thus be an optic capable of selecting at least one particular polarization; it may further allow light of other polarizations to pass through it unaltered in polarization state. For example, in the embodiment of FIG. 3, thepolarized light314 of transmitsource312 passes unaltered through thepolarization selector optic313. Depending on the transmitsource312 and thepolarization selector optic313 used, theselector313 can also serve the purpose of creating a linearly polarized beam at its output face. In these cases for example, transmitsource312 would emitnon-polarized light314 which, upon passing throughselector313, would become polarized.

In the embodiment of FIG. 3, light314 next encounters theretardation plate optic319. This optic319 is constructed and aligned to produce minimum reflections at its surface and to minimize transmission losses to the transmittedbeam314.Retardation plate optic319 could be any optic that is capable of rotating light (e.g. beam314), or more particularly, the polarization of light in a desired direction.

The transmittedbeam314 next passes throughlens316 alongoutbound beam path318. Theoutbound beam314 hits a target (an object in space such as, for example, a building, a bar code on the building or an identification unit mounted on the building). Theoutbound beam314 is reflected from the target and returns to thesystem300 via thesame beam path318. Incorporation ofpolarization selector optic313 andretardation plate319 allows a single beam path to be used for both transmitting and receiving light.

Light114 is now reflected light124.Return beam324 now passes throughlens316.Next return beam324 passes through theretardation plate319, which introduces another wave front phase retardation on thereturn beam324.

Thereturn beam324 now encounters thepolarization selector313. Since the polarization state of thereturn beam124 is now different to that originally transmitted by thepolarization selector313 in the form of theoutbound beam314, thereturn beam324 is directed by polarization selector towards thereceiver322.

Before reaching thereceiver322, the return beamencounters limiting aperture350. Limitingaperture350 may be placed in any position in thereturn beam path324 betweenlens316 andreceiver322. In one embodiment, limitingaperture350 is at or near the focal point of thelens316. The position of limitingaperture350 is intended to optimize the ratio between the spot size of a target and the spot size of an object blocking the target (such as blockage192) or an object behind the target (such as object194).

Receiver322 is any suitable substrate for receiving light, including for example, a silicon photo diode, photo cells, biological optical systems, radio receive systems, photo tubes and microwave receivers.

FIG. 4 shows a schematic view of another embodiment of anoptical system400 in accordance with the present invention. Such an optical system may be used in a dual-beam range-finding or sighting system.

As seen in FIG. 4, theoptical system400 of the present invention includes onebeam path418 for a transmit system (comprising one transmitsource412 transmitting onebeam414 through one lens416) and anotherbeam path428 for a receiving system (comprising a reflectedbeam424 passing through a second lens426 and being received by a receiver422).

In thedual beam system400 of FIG. 4, the transmitsource412 of the transmit system emits light that travels through thelens416. This light becomes the collimatedoutbound beam414. Theoutbound beam414 hits a target (an object in space such as, for example, a building, a bar code on the building or an identification unit mounted on the building). The outbound beam is reflected from the target and returns to thereceiver422 of the receiving system viabeam path428. As this reflectedbeam424 passes through lens426, it is refracted so that it comes to a focus atreceiver422. Limitingaperture450 is placed as shown withinsystem400.

System400 may also include a sighting system withlens436 andlens446. A second limitingaperture455 may be placed as shown in order to reduce aiming error on any of the detectors in the system. In a typical sighting system, the system is visual andlens436 andlens446 may be used in a manner similar to a telescope as is known in the art. However, in a mechanical sighting system, for example,lens436 may also serve as a receiver in a manner similar toreceiver422. Output from such a receiver may be sent automatically to a detection system (not shown.)

FIG. 5 shows a schematic view of another embodiment of anoptical system500 in accordance with the present invention. Such an optical system may be used in a scanning system.

As seen in FIG. 5, theoptical system500 of the present invention includes onebeam path518 for a transmit system, which comprises one scanning transmitsource512 transmitting onebeam514 through a firstbeam scanning optics530, through afirst lens516 and finally through a secondbeam scanning optics535.Optical system500 also includes anotherbeam path528 for a receiving system, which comprises a reflectedbeam524 passing through asecond lens526 and being received by ascanning receiver522.

In thedual beam system500 of FIG. 5, the transmitsource512 emits light that travels through thescanning optics530,535 and throughlens516. This light becomes the collimatedoutbound beam514. Theoutbound beam514 hits a target (an object in space such as, for example, a building, a bar code on the building or an identification unit mounted on the building). The outbound beam is reflected from the target and returns to thereceiver522 of thedual beam system500 viabeam path528. As this reflectedbeam524 passes throughlens526, it is refracted so that it comes to a focus atreceiver522. Limitingaperture550 is placed as shown.

The optical system of the present invention may be used in aiming, range-finding and scanning systems. Such systems are required to be as small, high performance, lightweight, and low cost as possible. Theoptical system100 in accordance with the present invention reduces the complexity and cost of presently available optics-based aiming, range-finding and scanning systems, while simultaneously improving the overall system performance, data acquisition speed, manufacturability, and decreasing the size, weight, and cost.

The optical systems of the present invention allow simultaneous reductions in all four dimensions of size, weight, complexity and cost. Range-finding systems incorporating the optical systems of the present invention are therefore made more attractive for broader, or mass market uses. The optical systems of the present invention can also be used in conjunction with technologies of range-finding and compass readings for determining relative position and, with the absolute positioning of GPS, in order to determine the location of remote structures.

Furthermore, the systems of the present invention offer the possibility of significantly reducing range finding system manufacturing costs by lowering parts numbers and the requisite fixtures for those eliminated parts. Such low cost, reduced size, reduced complexity, minimum weight systems could conceivably be used by police, fire, ambulance, or any other type of emergency service, overnight delivery services, postal service, utility services, pizza delivery, meter-reading, golf courses, railroads, military vehicles, as well as private use.

Other potential applications include, but are not limited to: enhanced or mobile 911; enhanced directory services; air-traffic control; automobile and transportation; automated mass transit; public and private telecommunications systems; construction; geophysical and geologic industries; entertainment; medical; sports; manufacturing; mapping; meteorological applications; forestry management; agricultural industry; mining industry; aviation and nautical industries; HVAC systems; enhanced earth-moving systems; warehouse inventory management; ESDA haz-mat registry; tourism; mobile Internet access; and integration of this system with other systems.

It should be appreciated that the embodiments described above are to be considered in all respects only illustrative and not restrictive. The scope of the invention is indicated by the following claims rather than by the foregoing description. All changes that come within the meaning and range of equivalents are to be embraced within their scope.

Claims (18)

We claim:

1. A range-finder comprising:

a range-finder housing;

a transmit source for transmitting light operably attached to the housing;

a first lens operably aligned with the transmit source to allow an outbound beam of light transmitted from the transmit source to pass through the first lens;

a first receiver operably positioned within the housing to receive a return beam of light reflected from an object,

a second lens operably aligned with the first receiver to allow the return beam of light to pass through the second lens before reaching the first receiver;

a first limiting aperture operably aligned with the first receiver to improve a signal to noise ratio of the return beam;

a third lens operably positioned within the housing to receive a sighting beam of light reflected from the object;

a fourth lens operably aligned with the third lens to allow the sighting beam of light to pass through the fourth lens before the sighting beam reaches the third lens; and

a second limiting aperture operably aligned with the third lens to receive the sighting beam before the sighting beam reaches the third lens.

2. The range-finder ofclaim 1 further comprising:

a second receiver operably positioned within the housing to receive a sighting beam of light reflected from the object, wherein the second receiver is operably aligned with the fourth lens to allow the sighting beam of light to pass through the fourth lens before the sighting beam reaches the second receiver.

3. A scanner comprising:

a housing;

a scanning transmit source for transmitting light operably attached to the housing, the scanning transmit source operably adapted to differentiate between an outbound beam of light and a return beam of light;

a first lens operably aligned with the transmit source to allow the outbound beam of light transmitted from the scanning transmit source to pass through the first lens;

a first scanning optics operatively aligned with the first lens to allow the outbound beam of light transmitted from the scanning transmit source to pass through the first scanning optics before passing through the first lens;

a second scanning optics operatively aligned with the first lens to allow the outbound beam of light transmitted from the scanning transmit source to pass through the second scanning optics after passing through the first lens;

a scanning receiver operably positioned within the housing to receive the return beam of light reflected from an object;

a second lens operably aligned with the scanning receiver to allow the return beam of light to pass through the second lens before reaching the scanning receiver; and

a first limiting aperture operably aligned with the scanning receiver to improve a signal to noise ratio of the return beam of light.

4. A reduced noise optical system for distance measurement, comprising:

a lens operably aligned with a transmit source in a first alignment, wherein the first alignment allows the lens to collimate an outbound beam of light transmitted from the transmit source through the lens;

a receiver operably aligned with the lens in the first alignment to receive a return beam of light reflected from an object in a first instance;

a limiting aperture operably aligned with the lens in the first alignment to improve the signal to noise ratio of the return beam, wherein the lens also focuses the return beam;

wherein the transmit source is a polarization selector operably aligned with the receiver to differentiate between the outbound and return beams based on polarization of the light.

5. The system ofclaim 4 further comprising:

a retardation plate operably aligned with the lens to allow the outbound beam to pass through the retardation plate and through the lens.

6. The system ofclaim 5 further comprising:

a selector positioned to allow the outbound beam to pass through the selector before passing through the retardation plate.

7. The system ofclaim 5 wherein the return beam passes through the retardation plate in a second instance before reaching the receiver.

8. The system ofclaim 4 wherein the transmit source is selected from the group consisting of: laser sources, incandescent sources, flourescent sources, microwave sources, semiconductor sources, maser sources and plasma sources.

9. The system ofclaim 4 wherein the receiver is selected from the group consisting of: semiconductor photo diodes, photocells, biological optical systems, radio receive systems, phototubes and microwave receivers.

10. A reduced noise optical system for scanning, comprising:

a lens operably aligned with a transmit source in a first alignment, wherein the lens collimates an outbound beam of light transmitted from the transmit source through the lens;

at least one scanning optic operably aligned with the lens in the first alignment;

a receiver operably aligned with the lens in the first alignment to receive a return beam of light reflected from an object, wherein the lens focuses the return beam;

a limiting aperture operably aligned with the lens to improve the signal to noise ratio of the return beam; and

a selector operably aligned with the receiver to differentiate between the outbound and return beams based on polarization of the beams.

11. The system ofclaim 10 wherein the transmit source is the selector.

12. The system ofclaim 10 further comprising:

a retardation plate operably aligned with the lens to allow the outbound beam of light transmitted from the transmit source to pass through the retardation plate and through the lens.

13. An optical system for distance measurement, comprising:

transmitting means for transmitting an outbound beam of light operably aligned with differentiating means for differentiating between the outbound beam and an inbound beam;

noise reducing means for improving a signal to noise ratio in the inbound beam;

rotating means for rotating polarization of at least one beam of light;

collimating means for collimating the outbound beam and focusing the inbound beam; and

receiving means for receiving the inbound beam.

14. The system ofclaim 13 wherein the transmitting means and the differentiating means are the same.

15. An apparatus for measuring distance comprising:

a housing;

a transmit source for transmitting light operably attached to the housing;

a retardation plate for rotating polarization of light operably attached to the housing, wherein an inbound beam of light reflected from an object passes through the retardation plate in a first instance;

a lens operably aligned with the retardation plate to collimate an outbound beam of light transmitted from the transmit source and to focus the inbound beam,

a receiver operably positioned within the housing to receive the inbound beam, wherein the inbound beam passes through the retardation plate in a second instance before reaching the receiver;

a limiting aperture operably aligned with the receiver to receive the inbound beam before the inbound beam reaches the receiver; and

a selector operably aligned with the receiver to differentiate between the inbound and outbound beams of light based on polarization of the inbound and outbound beams.

16. The apparatus ofclaim 15 wherein the transmit source, the retardation plate, the receiver and the selector are operably positioned in the same plane within the housing.

17. A method of measuring distance comprising the steps of:

transmitting an outbound beam of light, the outbound beam having a first polarization, from a transmit source to a retardation plate;

rotating the first polarization of the outbound beam with the retardation plate;

collimating the outbound beam through a lens to an object;

reflecting the outbound beam from the object back to the lens to focus the reflected beam;

passing the reflected beam from the lens to the retardation plate;

rotating polarization of the reflected beam so that the reflected beam has a second polarization;

selecting the reflected beam which has the second polarization;

sending the selected beam through a limiting aperture;

sending the selected beam from the limiting aperture to a receiver; and

measuring the distance to the object based on data from the receiver.

18. A method of transmitting light in a distance-measurement system comprising the steps of:

providing a transmit source substantially transparent to an inbound beam on a substrate;

providing a receiver on the same substrate;

transmitting an outbound beam of light, the outbound beam having a first polarization, from the transmit source to a retardation plate;

rotating the first polarization of the outbound beam with the retardation plate;

further transmitting the outbound beam through a lens to an object so that the lens collimates the outbound beam;

reflecting the outbound beam from the object back to the lens so that the lens focuses the reflected beam;

passing the reflected beam from the lens to the retardation plate;

rotating polarization of the reflected beam so that the reflected beam has a second polarization;

sending the selected beam to the receiver through the transmit source;

sending the selected beam to the receiver through a limiting aperture; and

sending the selected beam from the limiting aperture to a receiver.

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